Urinary lysosomal enzyme excretion after renal allotransplantation

Three urinary lysosomal enzymes, beta-glucuronidase (beta-Gluc), beta-galactosidase (beta-Gal) and N-acetyl-beta-D-glucosaminidase (NAG), were measured in twenty-one renal allograft recipients to evaluate their role in the diagnosis and prediction of rejection episodes, and in the prediction of eventual graft outcome. A fluorometric assay using methylumbelliferone substrates was used to measure the three enzymes in morning urine samples and enzyme activity was defined in terms of urine creatinine concentration. Urinary NAG levels increased significantly in 13/16 first rejection episodes and 4/4 instances of acute tubular necrosis and graft infarction. In 5 of the 16 first rejection episodes the NAG was predictive of the rejection. NAG was not useful in diagnosing second or subsequent rejections and beta-Gluc and beta-Gal were of little value in assessing any component of renal transplant pathology. As a prognostic index of eventual graft outcome, the peak urinary NAG was particularly encouraging. It correlated strongly with deterioration in graft function as time passed such that only 2/10 patients with peak NAG greater than 1400 Units had normal serum creatinines at 6 months post transplantation. Conversely 4/4 patients with peak NAG levels less than 700 Units had normal serum creatinine at that time. In our series the measurement of urinary NAG was a useful adjunct to the diagnosis of first rejections but appears to be more valuable in predicting graft outcome.